204 research outputs found
SearchCal: a Virtual Observatory tool for searching calibrators in optical long baseline interferometry. I: The bright object case
In long baseline interferometry, the raw fringe contrast must be calibrated
to obtain the true visibility and then those observables that can be
interpreted in terms of astrophysical parameters. The selection of suitable
calibration stars is crucial for obtaining the ultimate precision of
interferometric instruments like the VLTI. We have developed software SearchCal
that builds an evolutive catalog of stars suitable as calibrators within any
given user-defined angular distance and magnitude around the scientific target.
We present the first version of SearchCal dedicated to the bright-object case
V<=10; K<=5). Star catalogs available at the CDS are consulted via web
requests. They provide all the useful information for selecting of calibrators.
Missing photometries are computed with an accuracy of 0.1 mag and the missing
angular diameters are calculated with a precision better than 10%. For each
star the squared visibility is computed by taking the wavelength and the
maximum baseline of the foreseen observation into account.} SearchCal is
integrated into ASPRO, the interferometric observing preparation software
developed by the JMMC, available at the address: http://mariotti.fr
Magnetism, rotation and accretion in Herbig Ae-Be stars
Studies of stellar magnetism at the pre-main sequence phase can provide
important new insights into the detailed physics of the late stages of star
formation, and into the observed properties of main sequence stars. This is
especially true at intermediate stellar masses, where magnetic fields are
strong and globally organised, and therefore most amenable to direct study.
This talk reviews recent high-precision ESPaDOnS observations of pre-main
sequence Herbig Ae-Be stars, which are yielding qualitatively new information
about intermediate-mass stars: the origin and evolution of their magnetic
fields, the role of magnetic fields in generating their spectroscopic activity
and in mediating accretion in their late formative stages, and the factors
influencing their rotational angular momentum.Comment: 8 page
Far-Ultraviolet Dust Albedo Measurements in the Upper Scorpius Cloud Using the SPINR Sounding Rocket Experiment
The Spectrograph for Photometric Imaging with Numeric Reconstruction (SPINR)
sounding rocket experiment was launched on 2000 August 4 to record
far-ultraviolet (912-1450 A) spectral and spatial information for the giant
reflection nebula in the Upper Scorpius region. The data were divided into
three arbitrary bandpasses (912-1029 A, 1030-1200 A, and 1235-1450 A) for which
stellar and nebular flux levels were derived. These flux measurements were used
to constrain a radiative transfer model and to determine the dust albedo for
the Upper Scorpius region. The resulting albedos were 0.28+/-0.07 for the
912-1029 A bandpass, 0.33+/-0.07 for the 1030-1200 A bandpass, and 0.77+/-0.13
for the 1235-1450 A bandpass
Candidate X-ray-Emitting OB Stars in the Carina Nebula Identified Via Infrared Spectral Energy Distributions
We report the results of a new survey of massive, OB stars throughout the
Carina Nebula using the X-ray point source catalog provided by the Chandra
Carina Complex Project (CCCP) in conjunction with infrared (IR) photometry from
the Two Micron All-Sky Survey and the Spitzer Space Telescope Vela--Carina
survey. Mid-IR photometry is relatively unaffected by extinction, hence it
provides strong constraints on the luminosities of OB stars, assuming that
their association with the Carina Nebula, and hence their distance, is
confirmed. We fit model stellar atmospheres to the optical (UBV) and IR
spectral energy distributions (SEDs) of 182 OB stars with known spectral types
and measure the bolometric luminosity and extinction for each star. We find
that the extinction law measured toward the OB stars has two components:
Av=1--1.5 mag produced by foreground dust with a ratio of total-to-selective
absorption Rv=3.1 plus a contribution from local dust with Rv>4.0 in the Carina
molecular clouds that increases as Av increases. Using X-ray emission as a
strong indicator of association with Carina, we identify 94 candidate OB stars
with Lbol\geq10^4 Lsun by fitting their IR SEDs. If the candidate OB stars are
eventually confirmed by follow-up spectroscopic observations, the number of
cataloged OB stars in the Carina Nebula will increase by ~50%. Correcting for
incompleteness due to OB stars falling below the Lbol cutoff or the CCCP
detection limit, these results potentially double the size of the young massive
stellar population.Comment: 19 pages, 8 figures, accepted for the ApJS Special Issue on the
Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011.
All 16 CCCP Special Issue papers, including a version of this article with
high-quality figures, are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html (through 2011
at least
A Photometric Catalogue of Southern Emission-Line Stars
We present a catalogue of previously unpublished optical and infrared
photometry for a sample of 162 emission-line objects and shell stars visible
from the southern hemisphere. The data were obtained between 1978 and 1997 in
the Walraven (WULBV), Johnson/Cousins (UBV(RI)_c) and ESO and SAAO
near-infrared (JHKLM) photometric systems. Most of the observed objects are
Herbig Ae/Be (HAeBe) stars or HAeBe candidates appearing in the list of HAeBe
candidates of Th\'e et al. (1994), although several B[e] stars, LBVs and T
Tauri are also included in our sample. For many of the stars the data presented
here are the first photo-electric measurements in the literature. The resulting
catalogue consists of 1809 photometric measurements. Optical variability was
detected in 66 out of the 116 sources that were observed more than once. 15 out
of the 50 stars observed multiple times in the infrared showed variability at
2.2 microns (K band).Comment: 42 pages, no figures, to appear in Astronomy & Astrophysic
Cytoplasmic PML promotes TGF-β-associated epithelial–mesenchymal transition and invasion in prostate cancer
Epithelial–mesenchymal transition (EMT) is a key event that is involved in the invasion and dissemination of cancer cells. Although typically considered as having tumour-suppressive properties, transforming growth factor (TGF)-β signalling is altered during cancer and has been associated with the invasion of cancer cells and metastasis. In this study, we report a previously unknown role for the cytoplasmic promyelocytic leukaemia (cPML) tumour suppressor in TGF-β signalling-induced regulation of prostate cancer-associated EMT and invasion. We demonstrate that cPML promotes a mesenchymal phenotype and increases the invasiveness of prostate cancer cells. This event is associated with activation of TGF-β canonical signalling pathway through the induction of Sma and Mad related family 2 and 3 (SMAD2 and SMAD3) phosphorylation. Furthermore, the cytoplasmic localization of promyelocytic leukaemia (PML) is mediated by its nuclear export in a chromosomal maintenance 1 (CRM1)-dependent manner. This was clinically tested in prostate cancer tissue and shown that cytoplasmic PML and CRM1 co-expression correlates with reduced disease-specific survival. In summary, we provide evidence of dysfunctional TGF-β signalling occurring at an early stage in prostate cancer. We show that this disease pathway is mediated by cPML and CRM1 and results in a more aggressive cancer cell phenotype. We propose that the targeting of this pathway could be therapeutically exploited for clinical benefit
Low-resolution spectroscopy and spectral energy distributions of selected sources towards sigma Orionis
Aims: We investigated in detail nine sources in the direction of the young
sigma Orionis cluster, which is considered a unique site for studying stellar
and substellar formation. The nine sources were selected because of some
peculiar properties, such as extremely red infrared colours or too strong
Halpha emission for their blue optical colours. Methods: We took high-quality,
low-resolution spectroscopy (R ~ 500) of the nine targets with ALFOSC at the
Nordic Optical Telescope. We also re-analyzed [24]-band photometry from
MIPS/Spitzer and compiled the best photometry available at the ViJHKs passbands
and the four IRAC/Spitzer channels for constructing accurate spectral energy
distributions covering from 0.55 to 24 mum. Results: The nine targets were
classified into: one Herbig Ae/Be star with a scatterer edge-on disc, two
G-type stars, one X-ray flaring, early-M, young star with chromospheric Halpha
emission, one very low-mass, accreting, young spectroscopic binary, two young
objects at the brown dwarf boundary with the characteristics of classical T
Tauri stars, and two emission-line galaxies, one undergoing star formation, and
another one whose spectral energy distribution is dominated by an active
galactic nucleus. Besides, we discover three infrared sources associated to
overdensities in a cold cloud in the cluster centre. Conclusions:
Low-resolution spectroscopy and spectral energy distributions are a vital tool
for measuring the physical properties and the evolution of young stars and
candidates in the sigma Orionis cluster.Comment: Accepted for publication in A&
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